This introductory chapter makes the case for studying systems of ethical rules as an important historical phenomenon in their own right. It shows that both history and anthropology have tended to overlook the importance of rules in many ethical systems. It argues that this is due to a number of impulses within contemporary ethical and legal thought, including the move towards virtue ethics and an enduring distinction between the purviews of law and morality. Having established that the boundaries between law and morality are not as clear-cut as many assume, the Introduction sets out the case for thinking instead in terms of ‘ruly’ or legalistic ethics. It argues that rules can enable ethical life and coexist with virtue ethics. Finally, it argues for the retention for comparative purposes of the concepts of conscience and casuistry. Both have become too strongly identified with particular instances of the Christian tradition. When defined in broader terms as awareness of the moral dimensions of one’s actions, conscience can be reclaimed as a helpful concept, which allows us to interrogate complex problems such as dilemma and doubt. In the case of general rules, such problems arise precisely through the consideration of particular cases – or casuistry. These points made, the Introduction summarises the chapters that follow and sets out the arguments of the book as a whole: that rules can underpin and enable ethical life; that rules interact in important ways with virtue ethics; and that ‘ruly’ ethical systems engender moral rules about rules.